Screw feeder in a continuous cellulose digester

ABSTRACT

A SCREW FEEDER INSERTED IN THE OP OF A CELLULOSE DIGESTER COMPRISES A VERTICAL DRIVEN CENTER BODY WITH AN EXTERIOR HELICAL FLANGE SURROUNDED BY A SCREEN CASING. THE CENTER BODY IS TUBULAR AND OPEN AT BOTH ENDS, SO THAT FIBER MATERIAL CAN PASS AXIALLY THERETHROUGH. TWO FIBER MATERIAL INLETS ARE ALTERNATELY USED FOR SUPPLYING FIBER MATERIAL AND THE FEEDER SCREW IS REVERSIBLE, SO THAT IT MOVES THE FIBER MATERIAL EITHER DOWNWARDLY OR UPWARDLY PAST THE SCREEN. BY MEANS OF A SPIDER, THE UPPER END OF HE TUBULAR CENTER BODY IS ATTACHED TO A ROTARY VERTICAL SHAFT WHICH IS JOURNALED IN THE TOP OF THE DIGESTER, THE LEGS OF THE SPIDER LEAVE THE SUPPER END OF THE CENTER BODY OPEN.

J l 3, i973 uy J. c. F. c. RICHTER 3,743,572

SCREW FEEDER IN A CONTINUOUS CELLULOSE DIGESTER Filed June 9, 1971 2 Sheets-Sheet l Fig.

ffa/yfys SCREW FEEDER IN A CONTINUOUS CELLULOSE DIGESTEJR Filed vJune 9, 1971 July 3, 1973 J. c. F. c. RICHTER 2 Sheets-Sheet 2 79 Tran/VWS United. States Patent C Inf. cl. Dzic 7/06 U.S. Cl. 162-246 9 Claims ABSTRACT F THE DISCLOSURE A screw feeder inserted in the top of a cellulose digester comprises a vertical driven center body with an exterior helical flange surrounded by a screen casing. The center body is tubular and open at both ends, so that fiber material can pass axially therethrough. Two fiber material inlets are alternately used for supplying fiber material and the feeder screw is reversible, so that it moves the fiber material either downwardly or upwardly past the screen. By means of a spider, the upper end of the tubular center body is attached to a rotary vertical shaft which is journaled in the top of the digester. The legs of the spider leave the upper end of the center body open.

The invention relates to a screw feeder for charging fiber material into the top of a continuous cellulose digester, consisting of a driven vertical tubular center body provided with an exterior helical flange and arranged within a surrounding casing.

The object of the invention is to make the screw feeder alternately usable for one direction of rotation or the other. Normally the center body is turned in such a direction that its helical flange forces the fiber material downwardly, but particularly in cases where the digester top is steam-filled, it may be desirable to reverse the direction of rotation so that the fiber material is rst driven upwardly by said helical flange before it starts its descending motion towards the bottom of the digester.

According to the main feature of the present invention the constructive diiculties connected with said proposal are solved by making the lower end of the tubular center body open in order to enable the fiber material to pass also through the tubular interior of the center body. By utilizing in this manner also the core of the center body for transfer of fiber material the diameter measurement, else required, 0f the screw feeder as well as of the surrounding portion of the digester shell is reduced and it is possible by simple measures to adapt the screw feeder to one or the other way of operation.

A preferred embodiment of the screw feeder is diagrammatically shown in FIG. 1 and FIG. 2 in accompanying drawings, FIG. 1 referring to downward feed and FIG. 2 to upward feed.

As shown in the drawings, the screw feeder is placed inside the narrow cylindrical top portion 11 of a continuous cellulose digester adapted for downward motion of a suspension of fiber material in digesting liquor and discharge of digested pulp at the bottom of the digester. The design and the operation of said digester may essentially correspond to what is shown and described in the -U.S. patent specification No. 3,007,839.

The screw feeder comprises a center body or core 13 having the shape of a vertical tube placed centrally in the digester top and having on its outside a horizontally projecting flange 15 of constant width which runs like a screw thread several turns around the tube from one end thereof to the other. The tube 13 is open at both ends. By means of a spider consisting of e.g. four arms 16 and a hub 17 the upper end of said tube is attached to the lower end of a rotary vertical shaft 19 extending through a stuffing box 21 inserted in the bulb-shaped top cover 23 of the digester and connected to a geared driving motor 25.

Inserted between the digester shell 11 and the feeder screw 13, 15, is a tubular casing which closely surrounds the latter. Said casing has an upper impervious part 27 and a low part 28 which is perforated or slitted and forms a stationary cylindrical screen or strainer. Between the casing and the digester shell there is a chamber 29 for collection of liquid screened olf the fiber material, an outlet conduit 31 being connected to said chamber.

The liber material to be treated in the digester and consisting of wood chips, straw or other ligno-cellulosic material, is supplied as a suspension to the digester top through a conduit which alternately can be connected to two inlet fittings 35, 37 on the digester top, one being placed above and the other below the feeder screw and its surrounding casing. The inlet not used is closed by a blind flange 39 (FIG. l) or 41 (FIG. 2).

When the digester should operate under hydraulic pressure, i.e. without a steam or gas cushion at the top, the conduit 33 is connected to the upper inlet 35 and the feeder screw is turned in such a direction that the screw thread 15 forces the fiber material suspension downwardly. During the passage of the suspension along the screen 28 a great part of the liquid therein is separated olf and departs through the conduit 31, and the thickened solid material is pushed down through the neck of the digester. Part of the suspension may pass through the tubular interior space of the feeder screw without being thickened or positively driven. However, it is usually desirable to close said path land to this end there is provided a loose or easily detachable auxiliary means in the shape of a conical partition plate 43 which can be placed over the spider 16, 17, when required.

When it is desired instead to use the digester for steamphase digestion, the arrangement of the screw feeder as shown in FIG. 1 is not suitable, because steam from the digester top would pass through the Screen 28 and penetrate into the liquid return conduit 31. Therefore, according to an additional feature of the invention, said steam escape path may be closed by a loose or easily detachable auxiliary means which, when inserted, closes the space between the feeder screw and its screen casing 28 at the lower end. Said auxiliary means is formed by a detachable stationary partition arranged below and radially outside of the core of the feeder screw and having the shape of an annular flange 45 which is connected and sealed to the digester shell and which approaches the lower end of the rotary feeder screw as closely as possible. Attached to said annular ange 45 on the lower side is a short tube 47 for connection to the liber material inlet fitting 37 on the digester shell.

When the digester should be used for steam-phase digestion, the conduit 33 is connected to said inlet fitting 37, so that the fiber material suspension is supplied through the tube 47 to the space between the feeder screw 13 and the screen 28. The feeder screw is driven in such a direction that its helical flange 15 feeds the fiber material upwardly in said space. In the screen chamber 29 there is maintained a liquid level 48, and therefore the fiber material is lifted out of the liquid and is delivered drained to the upper end of the feeder screw. The partition 43 has been removed and the fiber material drops into the central interior space of the feeder screw and then through the same and into the steam-filled upper portion of the digester.. According to FIG. 2 the inlet fitting 35 is closed, but instead it may be used for admitting steam required for the digestion.

According to a further feature of the invention the outlet 31 is shut off from communication with the steam space in the digester top by means of a kind of a liquid lock which seals better to steam than what a movable seal between the feeder screw and the ange 45 would do. Said liquid lock is formed by a tubular partition 49 which projects upwardly within the interior space of the feeder screw and which has its lower end sealed to the digester shell by being connected to or made integral with the annular llange 4S. The tubular partition 49 extends in the axial direction beyond the screen 28 and to a level situated above the liquid level 48, preferably as far as to the upper end of the feeder screw. The gap between the inside of the feeder screw and said tubular partition 49 communicates on the lower side with the ber material inlet, and liquid will rise therein to the same level as in the screen chamber 29 and forms a lock preventing steam in the digester top from penetrating as far as to the screen 28 and from heating the liquid circulating through the conduits 33 and 31.

What is claimed is:

1. A screw feeder for charging fiber material into the top of a continuous cellulose digester, comprising:

a housing with an inlet for liber material;

a driven vertical tubular center body surrounded by the housing and coupled rotatably about its vertical axis with the housing, and an exterior helical flange disposed about the outer portion of the tubular center body for drawing fiber material from the inlet down between the housing and the tubular center body;

wherein the upper and lower ends of the tubular center body are open in order to also allow passage of fiber material from the inlet through the interior of the tubular center body.

2. The screw feeder as claimed in claim 1 further comprising a driving shaft journaled in the housing and a spider having legs joined at one end to the shaft and said legs coupled about the periphery of the top of said center body, said spider leaving the upper end of the center body substantially open.

3. The screw feeder as claimed in claim 2, comprising first auxiliary means detachably connected across the open spaces between the legs of the spider for covering these spaces when it in desired to close the interior passage through the tubular center body.

4. The screw feeder as claimed in claim 3, including second auxiliary means for closing the space betweeen the center body and the casing at the lower end, said second auxiliary means comprising a detachable annular partition arranged below and radially outside of the center body and having an inlet for fiber material connected to an underside thereof.

5. The screw feeder as claimed in claim 1 comprising:

a casing surrounding the tubular center body between the tubular center body and the housing, said casing having formed thereon a stationary cylindrical screen defining between the casing and the housing a screen chamber for collection of a liquid screened off from the liber material passing between the tubular center body and the casing, and

a tubular partition located concentric to the screen and extending in the axial direction beyond the screen toward the upper end of the feeder screw, said partition being detachably insertable into the tubular center body of the screw feeder and sealable to the housing below the lower end of the tubular center body, whereby when a certain liquid level is maintained in the screen chamber, leakage from the screen chamber into the interior of the digester through or past the screw feeder is prevented.

6. The screw feeder as claimed in claim 5, wherein said tubular partition is joined to the housing by an inner circular edge of said partition.

7. A device for withdrawing liquid from a ber material suspension charged into a continuous cellulose digester, comprising:

a housing with an inlet for the fiber material;

a cylindrical strainer surrounded by the housing; a

vertical rotatably driven feeder screw coupled rotatably about its vertical axis with the housing and located inside the strainer and coaxial therewith, said feeder screw comprising a tubular core and a helical flange attached about the outside thereof for advancing the fiber material suspension past said strainer as the feeder screw is rotated, said tubular core having open ends for passage of fiber material therethrough;

a screen chamber defined between the screen and a portion of a lower part of the housing;

and a conduit connected'to the screen chamber for discharging liquid passing through the strainer.

8. A dev ice as claimed in claim 7, further comprising:

a drive shaft extending through the top of the housing, a reversible motor connected to the upper end of said shaft, and a spider having legs at one end joined to the lower end of the shaft, said legs at the other end being coupled about the periphery of the top of said tubular core in such a manner as to allow passage of fiber material through the legs to the interior of said tubular feeder screw core.

9. A device as claimed in claim 7, further comprising a detachable annular plate extending radially from the housing to the immediate vicinity of the lower end of the tubular feeder screw core so as to prevent direct communication between the lower end part of the strainer and the interior of the digester, and an inlet conduit connected to said plate for supplying ber material suspension to the space surrounding the lower end of the feeder screw.

References Cited UNITED STATES PATENTS 3,074,842 1/ 1963 Strong l'62-237 X 2,459,180 1/ 1949 Richter 162-246 X 1,998,875 4/1935 Koda 162-52 S. LEON BASHORE, Primary Examiner R. V. FISHER, Assistant Examiner US. Cl. X.R. 

